static class Program
{
    static async Task<string> GetTaskAsync(int timeout)
    {
        Console.WriteLine("Task Thread: " + Thread.CurrentThread.ManagedThreadId);
        await Task.Delay(timeout);
        return timeout.ToString();
    }

    static async Task Main()
    {
        Console.WriteLine("Main Thread: " + Thread.CurrentThread.ManagedThreadId);

        Console.WriteLine("Should be greater than 5000");
        await Watch(NotParallel);
        Console.WriteLine("Should be less than 5000");
        await Watch(Parallel);
    }

    public static async Task Parallel()
    {
        var res1 = GetTaskAsync(2000);
        var res2 = GetTaskAsync(3000);

        Console.WriteLine("result: " + await res1 + await res2);
    }

    public static async Task NotParallel()
    {
        var res1 = await GetTaskAsync(2000);
        var res2 = await GetTaskAsync(3000);

        Console.WriteLine("result: " + res1 + res2);
    }

    private static async Task Watch(Func<Task> func) {
        var sw = new Stopwatch();
        sw.Start();

        await func?.Invoke();

        sw.Stop();
        Console.WriteLine("Elapsed: " + sw.ElapsedMilliseconds);
        Console.WriteLine("---------------");
    }
}